BitCoin Cash is a cryptocurrency resulting from a hard fork from Bitcoin in August 2017. It was forked just before Bitcoin had implemented SegWit, so, unlike Bitcoin, BCH doesn't include this feature. It has a block size limit of 8 MB, in contrast to Bitcoin's 1 MB. This allows for a much higher transaction throughput, i.e. 61 transactions per second, while Bitcoin is limited to 7. Also Bitcoin Cash's algorithm adjusts its difficulty every 6 blocks instead of 2016 blocks (Bitcoin).
Blockchain is a system of recording information in a way that makes it difficult or impossible to change, hack, or cheat the system. A blockchain is essentially a digital ledger of transactions that is duplicated and distributed across the entire network of computer systems on the blockchain. Each block in the chain contains a number of transactions, and every time a new transaction occurs on the blockchain, a record of that transaction is added to every participants ledger.
The decentralised database managed by multiple participants is known as Distributed Ledger Technology (DLT). Blockchain is a type of DLT in which transactions are recorded with an immutable cryptographic signature called a hash. This means if one block in one chain was changed, it would be immediately apparent it had been tampered with. If hackers wanted to corrupt a blockchain system, they would have to change every block in the chain, across all of the distributed versions of the chain. Blockchains such as Bitcoin and Ethereum are constantly and continually growing as blocks are being added to the chain, which significantly adds to the security of the ledger.